Memory Systems

How are short-term and working memory different?

Working memory is distinguished from short term memory by the very limited capacity, the need for repetition, and the very short duration

What type of memory is the amygdala involved in?

Memory for emotional experiences

How can procedural memory be tested in rats?

A variation of the radial arm maze The standard version is where rat learned to move efficiently as possible when retrieving food from each of baited arms of the maze (testing declarative memory). In the variation, small lights were illuminated above one or more arms containing food with unlit arm containing no food. Lights could be turned on/off at any time - optimal performance meant that the animal kept returning to retrieve food from lit arms as long as they were lit and avoided arms that weren't. Intended to draw on procedural memory because the consistent association between the presence of food and the illuminated lights. Rat did not have to remember which arms had been already explored - simply had to form a habit based on the association of the light with food

Systems consolidation

After synaptic consolidation, or perhaps overlapping with it in time, systems consolidation occurs in which engrams are moved gradually over time into distributed areas of the neocortex

Law of mass action

All cortical areas contribute equally to learning and memory. Memory cannot be localised. This has not proven to be incorrect

Dissociated amnesia

Amnesia not accompanied by any other cognitive deficit (ie the memory problems are dissociated from any other problems)

Developmental amnesia

Beth, Jon and Kate Hippocampus damaged perinatally (had complications at time of birth - brief periods where oxygen/blood supply to brain was compromised). Other brain structures intact. They were forgetful, but language acquisition and knowledge base (ie memory for facts) normal. Could not remember any episodes from their own lives (episodic memory). Suggests that the hippocampus required specifically for episodic memory, but not for semantic memory

What effects do large medial temporal lobe lesions have on DNMS?

Bilateral medial temporal lesions similar to that of H.M. (hippocampus, amygdala and cortex) cause delay dependent deficit. Short term memory (8-10s delay) intact, but long term memory (>15 s) impaired.

Describe Pavlov's classical conditioning experiment

Discovered and characterised in dogs by Ivan Pavlov Involves associating a stimulus that evokes a measurable response with a second stimulus that normally does not evoke this response. Training consisted of repeatedly pairing the presentation of the meat with the sound of the bell. After many of these pairings, the meat was withheld and the animal salivated to the sound alone. Dog had learned an association between the CS and the US

Describe the varying spatial scales of grid cells

Dorsal: - High resolution - Compact Ventral: - Lower resolution - Sparse

What are the problems with the standard model of memory consolidation?

Duration of retrograde amnesia Early accounts of HMs amnesia reported that his retrograde amnesia extended back a few years. An interpretation of this observation is that synaptic consolidation is complete quickly but systems consolidation takes years to complete and the retrograde memories HM lost were not "fully baked" - ie engrams still dependent on the hippocampus. Later studies on HMs retrograde amnesia showed that it extended back decades - perhaps systems consolidation is a very slow process that takes decades. However, this might not be the explanation as not so long ago humans only lived for a few decades. Later studies on HM suggested that he had retrograde amnesia for episodic memories that extended back virtually his entire life. This implies that the hippocampus, perhaps in concert with other medial temporal structures, may be involved with memories for a lifetime

Describe the virtual reality tests of episodic memory.

During exploration, subjects given different objects by different people in different rooms. During a later test session, ask one of four questions 1. Object: which one of these were you given? 2. Place: which of these objects were you given in this room? 3. Person: which of these objects was given to you by this person? 4. Order: which of these objects was given to you first?

What happens during electrical stimulation of the human medial temporal lobe?

Electrical stimulation of the temporal lobe sometimes produces memory-like experiences

What types of declarative memory are there?

Episodic memory: autobiographical life experiences Semantic: facts Note: declarative memory is also known as explicit memory (because it results form more conscious effort). These are often easy to form and are easily forgotten

What brain structure has shown to be active during reconsolidation?

Experiments looking at reconsolidation in humans have shown hippocampal activity in the reactivation condition

What structure is involved in cognitive maps?

Hippocampus

In what way are place fields dynamic?

If the box the animal is in is stretched along one axis, place fields will stretch in the same direction. Place rat into small box and let it explore, determine place fields of several cells, then cut a hole in one side of the box so animal can explore larger area. Initially there are no place fields outside the smaller box, but after the rat has explored its new expanded environment, some cells will develop place fields outside the smaller box. Cells seem to learn and alter their receptive fields to suit behavioural needs in the new larger environment

What is another term for non-declarative memory?

Implicit memory

What effects do specific lesions in the striatum have?

In rodents, lesions to striatum affect procedural but not declarative memory (they would have difficulties in the version of the radial arm maze that had arms lit, but not the task with all arms baited)

Anterograde amnesia

Inability to form new memories following brain trauma. If the anterograde amnesia is severe, a person might be completely incapable of learning and remembering anything new. In milder cases, learning may be slower and require more repetition than normal

Standard model of memory consolidation

Information comes through neocortex areas associated with sensory systems and is then sent to the medial temporal lobe for processing (especially the hippocampal system). It is in a variety of neocortical areas that permanent engrams are stored. Before systems consolidation, memory retrieval requires the hippocampus, but after systems consolidation is complete, the hippocampus is no longer needed

Where does the medial temporal lobe input originate from?

Inputs to the medial temporal lobe come from the association areas of the cerebral cortex. This contains highly processed info from all sensory modalities. The input contains complex representations (perhaps of behavioural important sensory info) rather than response to simple features such as light-dark borders.

What properties of hippocampal neurons aid them in their spatial navigation and memory?

John O'Keefe and colleagues at UCL showed that many neurons in the hippocampus selectively respond when a rat is in a particular location in its environment. This location (that evokes the greatest response) is called the neuron's place field and these neurons are called place cells.

What effect did the lesions have on H.M.?

Lesions had little effect on HMs perception, intelligence or personality. Instead, HM had anterograde amnesia and some degree of retrograde amnesia. His working memory and procedural memory were functional.

What structures support path integration?

Lesions of MEC or hippocampus disrupt path integration and thus may be necessary for it through activation of grid and place cells

Which parts of the brain where lesioned in H.M.?

Medial temporal lobe structures including: Hippocampus Amygdala Entorhinal, perirhinal and parahippocampal cortex

Collectively, what role do the medial temporal lobe structures play in memory?

Medial temporal structures are critical for the consolidation of memory

Retrograde amnesia

Memory loss for events prior to the trauma (forgetting this already known). In severe cases, there might be complete amnesia for all declarative information learned before the trauma. More often, follows a pattern in which events of the months or years preceding the trauma are forgotten, but memory is increasingly strong for older memories. Graded loss of old memories across time apparently reflects the changing nature of memory storage

Reconsolidation

Memory reconsolidation is the process of previously consolidated memories being recalled and actively consolidated. It is a distinct process that serves to maintain, strengthen and modify memories that are already stored in the long-term memory. During reconsolidation, memories become vulnerable to manipulation

How can procedural memory be tested in humans?

Mirror drawing task

What did the case of N.A. demonstrate about the function of diencephalic structures?

N.A. had an accident that caused a lesion in his left dorsomedial thalamus. Had anterograde and retrograde amnesia. Perseveration of short-term memory, recollection of old memories, and general intelligence. Suggested that diencephalic structures (which also connect to medial temporal structures) are part of a system serving the common function of memory consolidation.

Grid cells and their properties

Neurons in the medial entorhinal cortex (MEC - main input to hippocampus) discovered by Edvard and May-Britt Moser. These respond when the animal is at multiple locations that forma hexagonal grid. Cells in different portions of entorhinal cortex differ in the spacing between hotspots in the grid, but the sensitivity grid for each cell tiles the environment the rodent is in. There are different spatial scales (dorsal has high resolution and are compact, ventral has low resolution and are sparse) If a rat or human were to walk in various directions, grid cells would be activated more often and there would be more overall activity in the entorhinal cortex in some directions than others

What is the perirhinal cortex used for?

Object recognition Lesions impair ability to perform in DNMS task in a delay-dependent manner

Describe the delayed non-match to sample (DNMS) task

Often used on macaques. Monkey faces a table that has several small wells. It first sees the table with one object on it covering a well (ie a wooden block or chalkboard eraser - the sample stimulus). Monkey is trained to displace the object so it can grab a food reward in the well under the object. After getting the food, a screen prevents the monkey from seeing the table for some period of time (the delay interval). Finally, the animal gets to see the table again, but now there are two objects on it; one is the same as before and the other is new. In a DNMS task, the monkey's task is to displace the new object (the non-matching object) in order to get a food reward in the well below it (choice phase). Normal monkeys are relatively easy to train on the non-matching task and get very good at it (exploits their natural curiosity for novel objects). Memory required in the DNMS task has been called recognition memory (involves the ability to judge whether a stimulus has been seen before)

What experiments show the importance of the hippocampus for spatial memory?

Radial arm maze Morris water maze

Cognitive map theory

Proposed by O'Keefe and colleague Lynn Nadel States that the hippocampus is specialised for creating a spatial map of the environment

What role does the prefrontal cortex play in memory?

Required for short-term and working memory. The prefrontal cortex is also involved in problem solving and planning of behaviour

What structure is involved in route retrieval?

Right caudate nucleus

What diseases lead to deficits in procedural memory and what does this tell us about the structures involved in this type of memory?

Several diseases in humans attack the basal ganglia and certain effects on memory appear consistent with the striatum's role in procedural memory 1. Huntington's disease Kills neurons throughout the brain, but striatum is focus of attack. Shown to have difficulty learning tasks in which a motor response is associated with a stimulus (in addition to general motor dysfunction) 2. Parkinson's disease Degeneration of substantia nigra inputs to the striatum

What are the divisions of memory? What structures are involved?

Short term memory: frontal cortex Long term memory: can be further divided to declarative and non-declarative Declarative memory: can be further divided to episodic (involving hippocampus) and semantic memory (involving medial temporal cortex; perirhinal - objects) Non-declarative: can be further divided into priming, skills/habits and associative Priming: neocortex Skills/habits: striatum Associative learning can be further divided to skeletal musculature (cerebellum) and emotional responses (amygdala)

What structure is important for procedural memory?

Striatum

What evidence supports a hippocampal role in spatial navigation?

Studies of humans navigating space in video games and the streets of London suggest that the human hippocampus is important for spatial memory

What are memorisation techniques that can increase working memory?

Subtleties to the quantification of working memory capacity - More words can be held in memory if they are short common words - More words and numbers can be held in working memory if they can be chunked into meaningful groups There are trade-offs in the amount and the precision of stored info that are influenced by the behavioural significance of the information

Famous faces test

Test for retrograde amnesia

Conditioned response (CR)

The learned response to the conditioned stimulus

Korsakoff's syndrom

Usually resulting from chronic alcoholism. As a result of poor nutrition, alcoholics may develop a thiamin deficiency, which can lead to symptoms such as abnormal eye movements, loss of coordination and tremors. Thiamin deficiency can lead to structural brain damage that produces Korsakoff's syndrome. Usually lesions in the dorsomedial thalamus and the mammillary bodies

Describe the radial arm maze task

Version 1: Consists of arms or passageways, radiating from a central platform. If a normal rat is put in this maze, it will explore until it finds the food at the end of each arm. With practice, the rat becomes efficient at finding all the food, going down each arm of the maze just once. Rat uses visual or other cues around the maze to remember where it has already been. Tests spatial working memory and is impaired with hippocampal lesions. Version 2: Similar to above but lights are illuminated above arms where there's food. Rats don't have to remember which arms they've been down. Tests procedural memory and is impaired with lesions in the striatum.

Describe the connectivity in the medial temporal lobe

Sensory information -> Cortical association areas -> parahippocampal and rhinal cortical areas -> hippocampus (which feeds back to cortical association areas) -> (via fornix) thalamus, hypothalamus

Properties of place cells and place fields

1) A given place cell fires whenever the animal occupies a particular location within its environment (the place field) independent of the direction the animal is facing. 2) Multiple place cells cover the environment. Hippocampal place cells are thought to represent the spatial layout of an environment in a map-like way. Supports both cognitive mapping and path integration 3) Place fields are anchored to landmarks. Place cells are predominantly controlled by visual cues (ie local or distal landmarks, distance to environmental boundaries) 4) Firing is also updated when animal moves around in darkness (fires based on where animal thinks it is). So place cells also receive and can use non-visual information about self motion (vestibular, proprioceptive, motor efference copy)

What are some features of working memory

1. A system for the temporary maintenance and manipulation of information. Lasts on the order of seconds 2. Sharply limited in capacity and require rehearsal. Keeping a memory alive through repetition is a hallmark of working memory (ie remembering a phone number by repeating it) 3. Combines storage and processing, serves as a mental workspace for performing complex tasks 4. Commonly studied by measuring a person's digit span (max number of randomly chosen numbers a person can repeat back after hearing a list read). Normal digit span is seven +/- two 5. Draws on short term memory, long term memory and attention Working memory is a system for the temporary maintenance and manipulation of information. Combines storage and processing, and serves as a mental workspace for performing complex tasks

What have we learned from H.M. and other amnesiacs?

1. Ability to acquire new memories is a distinct function, separable from other perceptual and cognitive abilities. HMs perception and cognitive abilities are normal 2. Medial temporal lobes are not required for short term or working memory. HM can retain a number or a visual image for a short period after learning. He can carry on a normal conversation provided it doesn't last too long or move across too many topics 3. Medial temporal lobes are required for converting short term memories into long term memories (consolidation) HM cannot retain new information over long time periods 4. Medial temporal lobes are not the ultimate storage sites for long term memory of all previously acquired knowledge. HM can remember vividly some facts and events from his childhood

Name important research that has elucidated the role of the hippocampus in memory

1. Hippocampus is critical for memory consolidation of facts and events (H.M research) 2. Hippocampus is important for spatial memory (studies on rodents like Morris water maze and radial arm maze and people in virtual reality) 3. Hippocampus is required for episodic memory (virtual reality tests and developmental amnesiacs)

What does the idea of a cell assembly suggest about an engram?

1. It could be widely distributed among connections that link the cells of the assembly 2. It could involve the same neurons that are involved in sensation and perception 3. Destruction of only a fraction of the cells of the assembly would not be expected to eliminate the memory, possibly explaining Lashley's results

What are some features of short term memory

1. Short-term memory is information held by the brain only temporarily, on the order of hours. 2. It is vulnerable to disruption. For example, it can be erased by head trauma or electroconvulsive therapy (ECT) to treat psychiatric illness (which may not affect long-term memories). 3. Limited capacity (7 +/- 1 numbers, words, chunks) 4. Rapid input and retrieval 5. Not impaired in amnesia These observations led to the idea that facts and events are stored in short term memory and a subset are converted into long-term memories through memory consolidation

How is visual stimuli used for determining place fields/

Location of place field is related to sensory input such as visual stimuli in environment. For example, if you put certain images around the corners of the box such as a star above the northwest corner, take the rat out of the box and blindfold it, rotate the box and replace the rat, the neuron becomes active when the rat goes to the corner near the star. This demonstrates, that at least under some conditions, the response is based on visual input

What did the effects of H.M.'s lesions tell us?

Some or all of the structures damaged (hippocampus, amygdala and entorhinal, perirhinal and parahippocampal cortex) are required for formation of new long term declarative memories but not for short term and working memories or for new long term non-declarative memories (procedural memories).

Synaptic consolidation

Changes in synapses create a memory trace via this process

What are two types of associative learning?

Classical conditioning and instrumental (operant) conditioning

Describe an experiment showing that reconsolidation occurs in humans

College students were asked to memorise 20 objects that they were shown at one time and then placed in a basket. Each student practiced naming all items until they remembered at least 17. One day later (presumably after memory consolidation) some were given a reminder by showing them the empty basket and asking them to describe what happened the day before without naming objects (reactivating memories). Control group of students did not receive this reminder with hope of not reactivating this memory. Both the reminded and the not-reminded groups were then asked to memorise a second group of 20 objects on day 2. On day 3 of the experiment, all subjects were asked to recall the objects from the first group on day 1 of the study. On average, subjects recalled about 8 objects regardless of whether they had received a reminder on day 2. Subjects given the reminder on day 2 accidentally included numerous objects from day 2 in their recall whereas these intrusions rarely occurred in subjects not given reminder on day 2. Appears that the reminder may have served to reactivate the consolidated day 1 memories, making them labile again

Describe the Morris water maze

Commonly used test of spatial memory in rats Rat is placed in a pool filled with cloudy water, with a hidden platform that allows rat to escape. Rat placed in water the first time will swim around until it bumps into the hidden platform. Normal rats quickly learn the spatial location of the platform and on subsequent trials waste no time swimming straight to it. Once they figured out what to search for, rats put in a maze with a platform with a different location learn the task much faster. Animal can use external landmarks to locate the platform (platform is in a fixed location relative to platform). There are different start points, so animals cannot simply follow a route.

What disease can lead to memory loss or impaired ability to learn?

Concussion, chronic alcoholism, encephalitis, brain tumour and stroke can all disrupt memory More common for trauma to cause limited amnesia along with other non memory deficits rather than not knowing anything about themselves or their past. In clinical cases, there's often a mixture of retrograde and anterograde amnesias of different degrees of severity

What is the neural basis of route learning in humans?

Hartley et al. 2003 Cognitive map formation and use during fMRI in humans Training: freely explored complex virtual environment. Testing: found shortest route between two locations Control: followed same route but with different directions Route retrieval accuracy associated with activation of right caudate nucleus

What evidence shows that the hippocampus is involved in cognitive maps in humans?

Hartley et al. 2003 Neuron Cognitive map formation and use during fMRI in humans Training: freely explored complex virtual environment. Testing: found shortest route between two locations Control: followed same route but with different directions Wayfinding accuracy associated with activation of the hippocampus

Describe Karl Lashley's experiment

Conducted experiments to study the effects of brain lesions on learning in rats. Wanted to see if engrams reside in particular association areas of the cortex. He trained a rat to run through a maze to get a food reward. In the first trial, the rat was slow getting to the food because it would enter blind alleys and have to turn around. After running through the same maze repeatedly, rat learned to avoid blind alleys and go straight to food. Found that a rat given a brain lesion after it had learned to run the maze then made mistakes and went down blind alleys it had previously learned to avoid. Next, he wanted to see how the size and location of lesions affected learning and memory. Found that the severity of the deficits caused by the lesions (both for learning and memory) correlated to the size of the lesions. This was apparently unrelated to the location of the lesion within the cortex. Conclusion: He speculated that all cortical areas contribute equally (equipotential) to learning and memory and that the severity of impairment (Law of Mass Action). Implied that engrams are based on neural changes spread throughout the cortex rather than being localised to one area. However, this later proved to be wrong

What information do grid cells use?

Controlled by visual cues (landmarks) Controlled by self motion cues Combine information about distance and direction

Temporal order task

Cup is filled with sand and rat can dig into sand to find reward. Sand is mixed with a spice or herb (smells strongly). Five different cups of sand with different odours. Rat is presented with a single cup, then waits for 2.5 minutes and presented with the next cup. Encoding phase - sequence of five odours. Test phase Animal is presented with two different cups Rule is to dig through one presented first and there'll be food, but not the second one. Then perform a lesion (hippocampal or control lesion). Instead of two odours from sequences, have one from sequence and one from novel. Could still remember the smell, but couldn't remember the order (temporal as well as spatial component). Can conclude that the hippocampus is required for declarative memory that involves temporal information (order)

Priming and its features

Defined as an improvement in the ability to detect or identify words or objects after recent experience with them (ie word stem completion task) Unconscious (non-declarative) Can last a long time even after just one experience (priming for pictures can last a year) Does not require medial temporal lobe (HM) PET studies ahve shown that priming occurs very early in sensory pathway and is modality specific

What experiment can be used to test object recognition in monkeys?

Delayed non-match to sample task (DNMS)

What experiments can be used for testing short-term memory?

Delayed-response task

What experimental tasks would a patient with prefrontal lesions find difficult?

Delayed-response task Wisconsin Card Sorting Test Difficulty tracing a path through a maze (will repeatedly make the same mistakes)

How would a developmental amnesic patient perform in the virtual reality test of episodic memory?

Developmental amnesic patient Jon was not impaired on object test, but was impaired on person, place and time tests (aspects of episodic memory). Indicates a role for the hippocampus in episodic memory but not in object recognition

Instrumental conditioning

Discovered by Edward Thorndike An individual learns to associate a response (a motor act) with a meaningful stimulus (typically a reward such as food). For example, a rat is placed in a box with a lever that dispenses food. After accidentally hitting the lever a few times it learns that pressing the lever leads to a food reward, and will intentionally hit the lever to get food until it is no longer hungry. Thus, a predictive relationship is learned (subject learns that a particular behaviour is associated with a particular consequence). Motivation pays a large part and the underlying neural circuits are considered more complex than those involved in simple classical conditioning

Evidence of grid cells in humans

Doeller, Barry and Neil at UCL Human subjects navigated a virtual reality game while fMRI images of their brain activity were recorded. Recordings made showed a sinusoidal variation in the size of fMRI signal from the entorhinal cortex when subjects navigated in different directions around the clock - implies the presence of human gird cells have their hotspot aligned similarly in space. Like place cells, grid cells continue to fire when the animal is at the same grid locations even when lights are turned off

What evidence supports place cells in humans?

Ekstrom et al. 2013 Nature Intracortical recording in epileptic patients who are candidates for surgery while driving a taxi in a virtual town. Here only use visual cues.

What are some tasks that can be used to test retrograde memory in humans?

Famous faces test News events TV programmes Autobiographical memory interview

What evidence supports that prefrontal cortex is required for short term memory?

First evidence suggesting that the frontal lobe is important for learning and memory came from experiments performed using a delayed-response task: Monkey first shown food being placed in a well below one of two identical covers in a table. A delay period follows where the animal can't see the table. Finally the animal was allowed to see the table again and received the food as a reward if it chose the correct well. Large prefrontal lesions seriously degraded performance in this delayed response task, as well as other tasks including a delay period. Monkeys performed increasingly poorly as the delay period was lengthened. Implied that the prefrontal cortex may normally be involved in retaining information in working memory. More recent experiments suggest that the prefrontal cortex is involved with working memory for problem solving and the planning of behaviour

What is transient global amnesia and what can cause it?

Form of amnesia that involves a much shorter period of time. Sudden onset of anterograde amnesia that lasts for only a period of minutes to days, often accompanied by retrograde amnesia for recent events preceding the attack. Person may appear disoriented and ask same questions repeatedly, but is conscious and measures of working memory are normal. In a matter of hours, attack usually subsides and person is left with a permanent memory gap. Can be caused by brief cerebral ischemia (blood supply to brain reduced) or concussion. Can be brought on be seizures, physical stress, drugs, cold showers, and even sex (presumably because all of these affect cerebral blood flow)

What is the major output pathway of the hippocampus?

Fornix This loops around the thalamus before terminating in the hypothalamus

How might place cells generate their spatially selective activity?

From their connections to the entorhinal cortex. Models suggest that place fields in the hippocampus may result from he summation of inputs form grid cells. Single place field of a hippocampal neuron would be the location at which the grid locations of multiple input grid cells align.

Sequence learning task

Gradually learn a sequence of finger movements in resposne to a changing visual stimulus. Amnesic patients improve at the same rate, and are as good as controls. Striatum activated during task - magnitude of activation correlates with how much of the sequence the subject has acquired.

What are two types of non-associative learning?

Habituation (learning to ignore a stimulus that lacks meaning) and sensitisation (form of learning that intensifies your response to all stimuli, even ones that previously evoked little or no reaction)

What were Donald Hebb's ideas on how memories are stored and retrieved?

Hebb proposed that the internal representation of a stimulus consists of all the cortical cells that are activated by the external stimulus (cell assembly). These cells are connected in a reciprocal fashion. Hebb postulated that activation of this "cell assembly" causes reverberating activity in the interconnected cells - allows the stimulus to be remembered for a short period in working memory. Further hypothesised that if activation of the cell assembly persisted long enough, consolidation would occur by a "growth process" that made these reciprocal connections more effective, supporting long term memory (ie neurons that fire together wire together). If only a fraction of the cells of the assembly were activated by a later stimulus, the now-powerful reciprocal connections would cause the whole assembly to become active again, thus recalling the entire internal representation of the external stimulus.

What are key structures of the medial temporal lobe involved in memory?

Hippocampus Rhinal cortex (Entorhinal cortex and perirhinal cortex) Parahippocampal cortex

What role does the hippocampus play in memory?

Hippocampus is required for declarative memory for spatial information. Olton has also suggested it is necessary for working memory. Developmental amnesic patients suggest a role in episodic memory (the multiple trace model of memory suggests the hippocampus is always involved in retrieval and storage of these memories). Plays a critical role in binding sensory information for the purpose of memory consolidation. Supports spatial memory of the location of objects of behavioural importance. Involved in storage of memories for some length of time (duration is controversial). May form memories relating multiple things - specific facts, illustrations, interesting passages, arrangement of material on page and info about sounds events going on around you (interconnectedness is a key feature of declarative memory storage)

What effects did selective lesions have on DNMS task? What can be concluded from this? Lesions on: Hippocampus Amygdala Perirhinal cortex

Hippocampus: mild deficit Amgydala: no deficit Perirhinal cortex: severe deficit Perirhinal cortex critical for object recognition memory

What were some flaws in Lashley's experiments that led him to the wrong conclusion?

Lashley's experiments involved testing memory following lesions. He speculated that all cortical areas contribute equally to learning and memory (Law of Mass Action). One problem was that Lashley's lesions were large, each damaging multiple brain areas possibly involved in learning or remember the maze task. Another problem was that the rats may have solved the maze in several different ways (ie sight, feel, smell). Therefore, loss of one memory might have been compensated for by another. His conclusion that all cortical areas contribute equally to memory proved to be incorrect. However, his conclusion that all of the cortex participates in memory storage, and that an engram can be widely distributed in the brain, are correct

How long does working memory last?

Lasts on the order of seconds

Episodic memory

Memory for events Type of declarative memory

Semantic memory

Memory for facts Type of declarative memory

What structures are required for the DNMS task?

Mishkin et al. and Squire et al. demonstrated that severe deficits on the DNMS task result from bilateral medial temporal lesions in macaque monkeys. The perirhinal cortex, in particular, is responsible for object recognition in this task

Delayed response task

Monkey first shown food being placed in a well below one of two identical covers in a table. A delay period follows where the animal can't see the table. Finally the animal was allowed to see the table again and received the food as a reward if it chose the correct well. Large prefrontal lesions seriously degraded performance in this delayed response task, as well as other tasks including a delay period. Monkeys performed increasingly poorly as the delay period was lengthened. Implied that the prefrontal cortex may normally be involved in retaining information in working memory.

How is the place field determined without visual cues?

Once the animal has become familiar with the box with the images painted in each corner, a neuron will continue to fire when the rat goes in the northwest corner, even if the lights are turned off so it can't see location markers. Response of place cells are related to where the animal thinks it is. If there are obvious visual cues, the place fields will be based on these, if not place cells will still be location specific as long as the animal has had enough time to explore environment and develop a sense of where it is.

How will performance in the weather forecasting task differ between a PD patient and an amnesic patient?

PD patients have great difficulty learning the weather forecasting task but performed at normal levels on declarative memory questionnaire Amnesic patients had no trouble learning weather classification, but performed worse in questionnaire Suggest that the striatum in humans may play a role in procedural memory as part of system distinct from the medial temporal system used for declarative memory

What evidence is there for place cells in humans?

PET imaging studies show that the human hippocampus is activated in situations involving virtual or imagine navigation through the environment. Subjects were positioned in a PET machine while playing a video game. They could navigate a virtual town on the game monitor by using buttons. After learning their way around the virtual town, their brain activity was recorded while they navigated from an arbitrary starting point to a chosen destination. When person had to navigate environment, there was increased activation of the right hippocampus and the left tail of the caudate - hippocampus is particularly active in this spatial navigation task with humans. Caudate activation is thought to reflect movement and planning. Control condition - subjects moved through the virtual environment from the same start to finish, but arrows in the town pointed them in the correct direction (didn't need to think about navigation

What are some structures of Papez circuit?

Papez circuit is series of strongly interconnected structures that ring the diencephalon. Major component of this circuit is the fornix (bundle of axons that connects the hippocampus with the mammillary bodies in the hypothalamus). Mammillary bodies send a strong projection to the anterior nuclei of the thalamus. The dorsomedial nucleus of the thalamus also receives in put from the temporal lobe structures (including the amygdala and inferotemporal neocortex) and it projects virtually to all of the frontal cortex. * Damage to these connected diencephalic structures also cause amnesia

Describe the weather forecasting task

Patients saw one, two or three out of four possible cues. Had to guess whether this combination was arbitrarily associated with a prediction of sunny or rainy weather. For each patient, experimenter assigned different probabilities that various cues were associated with sun or rain. By being told when they guessed correctly or incorrectly about predicted weather, patients slowly built up an association between cues and weather. Draws on the formation of a stimulus-response habit In the second task, declarative memory was tested by having patients answer MC questions about the appearance of cues and the computer screen.

What area of the brain is required to succeed in the Wisconsin card-sorting task?

People with prefrontal lesions have great difficulty on this task when sorting category is changed, as they have deficits in working memory required for this task

What brain structure(s) is important for object recognition

Perirhinal cortex Anterograde amnesia resulting from perirhinal lesions is not specific to info from a particular sensory modality, reflecting convergence of input from association cortex of multiple sensory systems.

What did the case of Phineas Gage show about the role of the prefrontal cortex?

Phineas Gage had severe frontal lobe damage by an iron bar passing through the head, Gage had a difficult time maintaining a course of behaviour. Could carry out behaviours appropriate for different situations, he had difficulty planning and organising these behaviours. Showed that the prefrontal cortex is involved in working memory, allowing for problem solving and planning of behaviour

What are two types of procedural memory?

Procedural memory involves learning a motor response (procedure) in reaction to a sensory input. This occurs through two categories of learning: nonassociative learning and associative learning Note: Procedural memory is a form of non-declarative memory. Non-declarative memory usually requires repetition and practice over a longer period of time, but are less likely to be forgotten

What is the multiple trace model of consolidation and how might it explain some properties of amnesia?

Proposed by Lynn Nadel and Morris Moscovitch Proposed as a way to avoid the necessity of the decades-long systems consolidation processs the standard model needs to account for extended retrograde amnesia. Perhaps the hippocampus is always involved in memory storage. Systems consolidation does not ever relinquish engrams entirely to neocortex. Engrams involve neocortex, but even old memories also involve the hippocampus. Each time an episodic memory is retrieved, it occurs in a context different from the initial experience and the recalled information combines with new sensory input to form a new memory trace involving both the hippocampus and neocortex. Creation of multiple memory traces presumably gives the memory a more solid foundation and makes it easier to recall. Because retrieval requires the hippocampus, complete loss of the hippocampus should cause retrograde amnesia for all episodic memories no matter how old. If there is partial damage, then the memories that are intact wold be the ones with multiple traces. Older memories would have been recalled more times, they would be more likely to survive hippocampal damage and this would give rise to a temporal gradient in retrograde amnesia

What experimental tasks may utilise place cells

Radial arm maze Morris water maze If hippocampal place cells are involved in running the maze, it makes sense that performance is degraded by destroying the hippocampus

What effect does a hippocampal lesion have on the radial arm task

Rat can learn to go down arms of maze and eat food placed at each arm, but they never learn to do this efficiently. They go down the same arms more than once and leave other arms containing food unexplored for an abnormally long time. Additionally, if you place food only at certain arms, they are able to learn to avoid arms that never contain food but still not able to get food from other arms efficiently. No-food arms are memorised as part of the "procedure". This shows they're procedural memories are intact, but their working memory (presumably used to retain information about which arms have been visited) isn't

Describe the odour discrimination task and the response of hippocampal neurons.

Rat's cage has two distinct odors from different ports. For each pair of odours, the animal was trained to go towards the port releasing one odour and to avoid the other port. Some neurons in the hippocampus became selectively responsive for certain pairs of odours. Neurons were particular about which odour was at each port - they would respond to odour 1 at port A and odour 2 at port B, but not when odours had switched ports. Indicates that the response to the hippocampal neurons related specific odours, their spatial locations and whether they were presented separately or together. Hippocampal lesions produced deficits on this discrimination task.

Describe the experiment and results of conditioning combined with electroconvulsive shock (ECS)

Rats trained by presenting a loud noise followed by a foot shock. Trained rats subsequently fear a shock when they hear a noise. After the loud noise, UC rats licked rapidly from a drinking tube but trained rats drank slower (indication that they feared the foot shock). If an animals was conditioned but immediately given electroconvulsive shock, it would lick quickly the next day as if it hadn't been conditioned - evidence for retrograde amnesia for conditioning. If there was a delay of 24 hrs, there was no fear attenuation - fear memory had been consolidated and amnesia for the conditioning could no longer be caused by ECS. On second day of experiment (after consolidation of fear memory) some of the conditioned animals were presented the loud noise immediately followed by the ECS. On the third day of the experiment, rats were tested once more. Rats that had received the noise-foot shock combination on the second day licked as much as rats that received ECS on the first day immediately after training (amnesic animals) Results suggest that the sound on the second day reactivated the fear memory, and once reactivated, this memory was wiped out by ECS. If memory was not reactivated (the animals that got ECS on the second day but without loud sound), then ECS had no effect. Suggests that reactivating a memory makes it sensitive just as it had been immediately after the memory was first formed (before consolidation)

How do hippocampal lesions affect performance in Morris water maze? What does this tell us about the role of the hippocampus?

Rats with bilateral hippocampal damage never seem to figure out the game or remember the location of the platform. This ability is not impaired if the platform is visible. Hippocampal computations are vital to allocentric place learning (cognitive mapping)

What are some tasks that can be used to test anterograde memory in humans?

Recall and recognition tests with words or pictures Word recall: Study phase: read words in list and try to remember Short term memory test - recall Distractor test - count vowels in certain words Memory test - recognition test phase Picture recall Try to redraw image

Autobiographical memory interview

Test for retrograde amnesia Ask people to remember specific information from a range of time periods. Factual questions probing personal information. Also asked to recollect a specific personal event for each time period. Taps into both semantic memory (facts) and episodic memory (events)

Wisconsin card-sorting test

Test for working memory Person is asked to sort a deck of cards with a variable number of coloured geometric shapes. Can be sorted by colour, shape, or the number of symbols, but at the beginning of the test, the subject isn't told which category to use. Subject begins putting cards into stacks and is informed when errors occur, by which the subject learns what sorting category is to be used. After 10 correct placements have been made, the sorting category is changed and the subject starts over again. To perform well on this test, a person must use memory of previous cards and errors in order to plan next card placement.

What role does the basal ganglia have in memory?

The basal ganglia is important for the control of voluntary movements. Two elements of basal ganglia are the caudate nucleus and putamen (together called the striatum). Several lines of evidence in studies of rodents and humans suggest that the striatum is critical for the procedural memory involved in forming behavioural habits.

Place field

The location that evokes the greatest response of a place cells

Conditional stimulus (CS)

The stimulus that normally does not evoke this same response because this one requires training (conditioning) before it will yield this response Ie auditory stimulus such as the sound of a bell

Unconditioned stimulus (US)

The stimulus that normally evokes the response because no training (conditioning) is required for it to yield a response Ie piece of meat causes the dog to salivate

What are the neuronal responses of a prefrontal cortex cell in an animal performing the delayed-response task?

There are neurons that are responsive when the animal sees the food reward and when it seems them again after a delay (simply correlates with visual stimulation). There are separate neurons, which fire only during the delay interval. Increased activity during the delay period may be related to the retention of information needed to make the correct choice after the delay (ie working memory)